Resins, in particular hydrocarbon resins, are additives which have been known for a long time for rubber blends for treads of vehicle pneumatic tires. They serve above all as processing auxiliaries and cause the necessary green tack of the rubber blends. Furthermore, certain vulkanisate properties, such as hardness, modulus and swelling properties, can be influenced by resins. They can also be employed as vulcanization resins or adhesion promoters. Typical bonding resins employed in the rubber industry are, for example petroleum resins, terpene resins, colophony resins, phenol-formaldehyde resins and coumarone-indene resins.
Resins from alpha-methylstyrene are known as additives for rubber blends. The use of resins based on alpha-methylstyrene in rubber blends is thus described e.g. in EP 2412731 A1, EP 1559586 A1 and DE 60201595 T2. These publications are concerned with the properties of the rubber blends disclosed therein with respect to at least one of the requirements in the tire, such as abrasion resistance, rolling resistance and wet grip, the rubber blends comprising up to 15 phr of the resin.
In the prior art limits are imposed on the use of relatively large amounts of resin due to the limited solubility in the polymer system of the particular rubber blend.
US/2012/0016056 A1 discloses, for example, a rubber blend for treads having silica as the main filler component, which comprises not more than 25 phr of a resin from alpha-methylstyrene and styrene. The resin here is premixed together with oil in order to improve the distribution of the resin in the polymer. This rubber blend is said to show an improvement with respect to rolling resistance properties, wet grip properties, abrasion resistance and handling properties.
WO 2012/062534 A1 and EP 0899297 describe, for example, rubber blends which can comprise up to 50 phr of a hydrocarbon resin. These rubber blends are said to solve the target conflict of rolling resistance and/or abrasion versus wet grip at a higher level, the rubber blends disclosed in the examples also here comprising only up to 15 phr of the particular hydrocarbon resin. In the examples disclosed all the blends comprise exclusively carbon black (70 phr) as a filler.